全文获取类型
收费全文 | 1555825篇 |
免费 | 26021篇 |
国内免费 | 7047篇 |
专业分类
电工技术 | 35176篇 |
综合类 | 6444篇 |
化学工业 | 275097篇 |
金属工艺 | 65885篇 |
机械仪表 | 45630篇 |
建筑科学 | 47236篇 |
矿业工程 | 11832篇 |
能源动力 | 50401篇 |
轻工业 | 118157篇 |
水利工程 | 15832篇 |
石油天然气 | 38358篇 |
武器工业 | 147篇 |
无线电 | 199206篇 |
一般工业技术 | 294372篇 |
冶金工业 | 178268篇 |
原子能技术 | 34622篇 |
自动化技术 | 172230篇 |
出版年
2021年 | 15560篇 |
2020年 | 11871篇 |
2019年 | 14652篇 |
2018年 | 18499篇 |
2017年 | 18293篇 |
2016年 | 22632篇 |
2015年 | 17513篇 |
2014年 | 28643篇 |
2013年 | 87916篇 |
2012年 | 37205篇 |
2011年 | 51887篇 |
2010年 | 45343篇 |
2009年 | 53326篇 |
2008年 | 47732篇 |
2007年 | 45590篇 |
2006年 | 45784篇 |
2005年 | 41625篇 |
2004年 | 42935篇 |
2003年 | 42622篇 |
2002年 | 41424篇 |
2001年 | 37969篇 |
2000年 | 36334篇 |
1999年 | 35448篇 |
1998年 | 49174篇 |
1997年 | 41941篇 |
1996年 | 37007篇 |
1995年 | 31750篇 |
1994年 | 29571篇 |
1993年 | 29407篇 |
1992年 | 26442篇 |
1991年 | 23604篇 |
1990年 | 23952篇 |
1989年 | 23040篇 |
1988年 | 21543篇 |
1987年 | 19791篇 |
1986年 | 19150篇 |
1985年 | 22499篇 |
1984年 | 22489篇 |
1983年 | 20481篇 |
1982年 | 19386篇 |
1981年 | 19458篇 |
1980年 | 18097篇 |
1979年 | 18610篇 |
1978年 | 17840篇 |
1977年 | 17798篇 |
1976年 | 18961篇 |
1975年 | 16091篇 |
1974年 | 15567篇 |
1973年 | 15682篇 |
1972年 | 13147篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
841.
J. B. Quinn G. E. Schumacher L. W. Schultheis 《Journal of Failure Analysis and Prevention》2004,4(1):41-46
Several days after heart surgery, a patient discovered his upper right canine tooth had broken at the root. Such tooth damage,
recognized post-operatively, is usually assumed to be caused by blunt mechanical force from an instrument used by the anesthesiologist
during placement of a breathing tube at the start of surgery.
In this case, the patient had saved the crown portion of the broken tooth, and it was possible to examine the root fracture
characteristics. The curvature and direction of the crack path and natural tooth situation suggested that failure could be
described through a cantilever beam model. This was confirmed when a whole extracted sample tooth was embedded and broken
by a measured force in a manner consistent with the model. The resulting fracture surface matched that of the patient’s broken
canine tooth. However, the high load and force direction necessary to fracture the root was inconsistent with forces applied
during the anesthesia procedure. The failure analysis and further investigation indicated tooth clenching on the breathing
tube during recovery was the likely cause of fracture.
This paper presents an alternate explanation for intubation-related dental injury, demonstrates the practicality of fractographic
analysis of biological materials, and introduces a methodology for simulating in vitro tooth settings for mechanical testing. 相似文献
842.
We report on picosecond time resolved spectroscopy of photogenerated infrared active vibrations in thin films of 2,5-dioctyloxy poly(phenylene vinylene). We excited the films by ?4 ps long pulses of 565 nm laser light with 2×1013 photons/cm2 per pulse and repetition rate of 76 MHz. We then followed the temporal evolution of the infrared active vibrational (IRAV) spectrum using a subsequent, variably delayed, weak tunable IR probe pulses of similar temporal duration. Under these conditions, we show clear spectroscopic evidence for photogenerated infrared active vibrations at times which are shorter than our temporal resolution (<4 ps). We suggest that the transient IRAV absorption is due to secondary polarons formation following exciton dissociation. 相似文献
843.
Mathematical models of thermomechanical processes which are based on the laws of rational thermodynamics of irreversible processes are treated. Singular features of the unsteady-state behavior of a continuous medium are demonstrated within different models, such as a medium with internal parameters of state, a medium with memory, and a medium of the velocity type. 相似文献
844.
Meghelli M. Rylyakov A.V. Zier S.J. Sorna M. Friedman D. 《Solid-State Circuits, IEEE Journal of》2003,38(12):2147-2154
A 43-Gb/s receiver (Rx) and transmitter (Tx) chip set for SONET OC-768 transmission systems is reported. Both ICs are implemented in a 0.18-/spl mu/m SiGe BiCMOS technology featuring 120-GHz f/sub T/ and 100 GHz f/sub max/. The Rx includes a limiting amplifier, a half-rate clock and data recovery unit, a 1:4 demultiplexer, a frequency acquisition aid, and a frequency lock detector. Input sensitivity for a bit-error rate less than 10/sup -9/ is 40 mV and jitter generation better than 230 fs rms. The IC dissipates 2.4 W from a -3.6-V supply voltage. The Tx integrates a half-rate clock multiplier unit with a 4:1 multiplexer. Measured clock jitter generation is better than 170 fs rms. The IC consumes 2.3 W from a -3.6-V supply voltage. 相似文献
845.
846.
L. A. Dombrovskii 《High Temperature》2003,41(6):819-824
Theoretical models of heat transfer by radiation through a vapor gap under conditions of film boiling of liquid are treated, namely, a general wave model for a gap of arbitrary thickness and an approximate model of geometrical optics. Calculations are performed of heat transfer by radiation under conditions of film boiling of water on hot surfaces of refractory metal and molten oxide. Practical recommendations are given to calculate the distribution of the power of absorbed radiation in a water layer. 相似文献
847.
848.
M. Riad Manaa Laurence E. Fried Evan J. Reed 《Journal of Computer-Aided Materials Design》2003,10(2):75-97
In this article, we review recent atomistic computational techniques to study the electronic structure aspects and chemistry
of energetic materials at high-pressure and/or high temperature. While several mechanisms have been proposed for the initial
events of energetic materials at high-pressure, we explore the validity of a proposed shear-induced local metallization via
molecular bond bending in the insensitive explosive TATB. We study the effect of high-stress (both uniform and uniaxial) on
the electronic energy band-gap and the first chemical event of a prototypical energetic material, that of nitromethane. We
also determine chemical reactions rate laws and decomposition mechanisms from a quantum-based molecular dynamics simulation
of HMX, a widely used explosive material, at conditions of high density and temperature similar to that encounter under detonation.
Finally, we review a new multi-scale computational tool recently developed to model the shock-induced chemistry of energetic
materials at the atomistic level, and report its applicability to shocked solid nitromethane.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
849.
Th. Heins 《e & i Elektrotechnik und Informationstechnik》2003,120(11):400-401
An enterprise is not just a tall shiny building or a collection of facilities. Rather, it is the sum of individuals collectively engaged in a common pursuit. From an information and communications perspective, this realization changes everything. By looking at the enterprise as a boundary-less collection of individuals who sometimes work in an office, sometimes at home, and sometimes on the road, we need new communications concepts designed to work with and enhance our complex home and work lives. 相似文献
850.
In this practical case study the method of self-organizing map (SOM) neural net is applied to analyze a CMOS process problem, where the device under study is a heartbeat rate monitor integrated circuit. The wafer yield is analyzed against the process control monitoring (PCM) parameter measurement values. The SOM efficiently reduces the parameter space dimensions and helps in visualizing the different parameter relations. This makes it possible to identify the most probable PCM parameters affecting the yield. Those were found out to be NMOS transistor drain current and aluminium sheet resistance. 相似文献